[PATCH] D119516: [RISCV] Add test case for a vsetvli insertion bug found after D118667.

[Craig Topper via Phabricator via llvm-commits]

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We're missing a vsetvli before a vse after a redsum in this test.

This appears to be because the vmv.s.x has a VL of 1, but did not
trigger a vsetvli because it is a scalar move op and any non-zero
VL would work. So it looked at it the predecessors and decided it was
that they all had a non-zero vl. Then the redsum was visited, it
also took the VL from the predecessors since the vmv.s.x and the 4
was found compatible.

Finally we visit the vse and it looks at the BBLocalInfo and sees
that is compatible because it contains a VL of 1 from the vmv.s.x,
the first instruction in the block. BBLocalInfo was not updated
when the vredsum was visited because BBLocalInfo was valid and no
vsetvli was generated.

I think fundamentally the vmv.s.x optimization has the same first
phase and third phase not matching problem that D118667 <https://reviews.llvm.org/D118667> was trying
to fix for stores.

This bug exists in the LLVM 14 release and I'm not sure what the
best fix for that is.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D119516

Files:
  llvm/test/CodeGen/RISCV/rvv/vsetvli-insert-crossbb.mir

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